briggs



Jan. 24, 1956 T. H, BRIGGS, JR 2,732,512

ELECTRON TUBE STRUCTURE Filed Oct. 15, 1952 9 I6 I wum 34 34 m INVENTOR THOMAS H. BRIGGS JR.

ATTORNEY United States Patent 7 2,732,512 ELECTRON TUBE STRUCTURE Thomas H. Briggs, Jr., Norristown, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application October 15, 1952, Serial No. 314,917

14 Claims. (Cl. 313-85) This invention relates to thermionic discharge tubes and more particularly it relates to disc cathode assem blies of the type generally utilized in cathode ray tubes and their method of construction.

Cathode assemblies in cathode ray tubes have conventionally been made with seamless tubing having a closed cylindrical cap at one end and a heater assembly inside. The assemblies have been supported by ceramic discs made of molded and fired porcelain or steatite. Such supports may be molded and machined to a high degree of accuracy. The accuracy of mechanical placement of the electron gun in a cathode ray tube therefore in the prior art primarily depended upon the method of affixing the cathode assembly to the ceramic supports. With seamless tubing, complicated swaging or embossing machinery is necessary to fasten the ceramic support to the cathode assembly, and once the process of fastening the cathode assembly to the ceramic supports of the prior air is completed there should be a way to precisely determine the spacing of the elements to allow for manufacturing tolerances in the fastening process.

Thermal efiiciency is lower than desired where a heater coil is inserted into a cathode tubing of the type described because of the relatively large non-emissive areas which must be heated and because of the poor thermal contact between the tubing and the heater coil. Large nonemissive metallic areas of complex structures of thermionic cathodes may, in addition, sublime and thereby cause a metallic coating on the ceramic insulatingmaterials generally used which decreases resistance and thus may cause electrical breakdown. By using a ceramic heater assembly the necessary heated metallic surface areas are reduced thereby further decreasing the amount of sublimation. When greater efl'iciency-is obtained the heater temperature becomes lower and the sublimation problem is lessened. Contamination of the emission coating may result when many operational steps are. required in assembly and a multiplicity of parts is necessary. This also may increase the cost and the spoilage.

Accordingly it is a primary object of the invention to provide an improved cathode assembly and its method of construction.

A more specific object of the invention is to provide a therminonic cathode assembly having high thermal efi'iciency. I

Another object of the invention is to provide an easily assembled thermionic cathode unit adapted to maintain very close dimensional tolerances and having few parts easily assembled in a minimum of steps.

A further object of the invention is to provide thermally eflicient lower heater temperature cathode structures which are relatively free from sublimation.

Other objects and features of advantage of the present invention will be found throughout the following description of the invention.

In accordance with the present invention a cathode assembly is provided with ametallic grid aperture cup, an

insulating disc having integral annular ridges for spacing 2,732,512 Patented Jan. 24, 1956 it from the bottom ofthe aperture cup, and a heater cathode assembly afiixed to the disc by -Alundum cement to thereby determine the distance between the cathode and grid aperture.

For more clearly understanding the nature and construction of the invention, the following more detailed description may be referred to in connection with the accompanying drawings, in which:

Fig. 1 is a sectional view of a cathode assembly embodying the invention;

, Fig. 2 is a partial sectional view of a modification of Fig. 1;

Figs. Sa'and 3b are respectively partial elevation and plan views of cathode assemblies constructed in accordance with the invention; 7 I

Figs. 4 and S are partial elevation section views of further embodiments of the invention;

Fig. 6 is a side elevationview of a sub-assembly constructed in accordance withthe teachings of the invention; and

Fig. 7 is an elevation view in section of a thermionic tube assembly constructed in accordance with a further phase of the invention.

Referring now more particularly to the drawing, where in like reference characters represent like component parts throughout several views, certain novel structural features of the invention are shown in Fig. 1. The assembly shown is for a disc cathode application such as conventionally used in the cathode ray tube art. Accordingly, a grid aperture cup 10 or liketube electrode is 'provided which has its grid aperture 12 in the bottom of the cup and lances 14 in the walls of the cup to hold an insulating disc spacer 16 in place'against the bottom of the cup 16 by means of integral annular spacer ridges 18 extending circumferentially about the grid aperture 12. The disc spacer which is preferably of ceramic material has a central aperture coaXially aligned with the grid aperture 12. A heater cathode assembly is afiixed in the aperture of the disc 16 by means of the well known bidized ceramic material of the type described in the Palumbo Patent 2,487,581. Such a heater is comprised of a porous ceramic material carbidized in a hydrocarbon atmosphere so that it can be heated by self-resistance to temperatures of 1,000 C. or more. Such ceramics provide a long life as heater elements. The cemented heating leads can be subjected to the same carbidizing process as the ceramics to assure good electrical contact.

A barium-oxide or like emissive coating may be applied directly to the carbidized ceramic base in the vicinity of the grid aperture aforedescribed to provide the necessary thermal emissive characteristics. However, in the preferred embodiment it is desirable to insulate the cathode and heater structures by a ceramic insulating cement layer 24 such as 'Alundum for holding a cathode structure 26 in intimate thermalcontact with the heater body 20. In this manner such great'thermal efiiciency is attained that the heater may be operated at lower temperatures and there is relatively little sublimation.

*efiicient and therforethe temperature of the heater body may be lower than that usually encountered in thermionic tubes. g I

In considering the described cathode assembly it is noted that the lances 14 in the grid cup walls securely hold the ridges 18 of the ceramic disc against the bottom of the cup. Accordingly, cathode assembly 20, 28 may be precisely cemented into the disc spacer aperture to establish the necessary close tolerances in the grid cathode spacing. Should any manufacturing tolerances occur in the cementing process they may be readily corrected by grinding of the ridges 18 to establish a precise tolerance control. In addition to the close dimensional tolerances that may be realized with the present assembly, the structure is simple and inexpensive to construct or assemble, requiring few parts as compared with conventional commercial assemblies. In this structure, the amount of metal is substantially reduced, thereby reducing any sublimation after long periods of operation at operating temperatures.

The spacer disc 16 may be held to the walls of the grid aperture cup 10 by means of embossed ridges 15 in the walls of the cup as shown in Fig. 2 if desired rather than by the lances of Fig. 1.. Thus, the metallic portions are insulated from the heater body to prevent any unnecessarily high temperature at which sublimation may occur. Likewise the structures of Fig. 3a or 3b may be utilized if necessary to reduce the thermal contact from the heater body 20 to the spacer disc 16, thereby keeping the metallic grid aperture cup at a lower operating temperature.

Maximum thermal contact is, however, provided between the cathode 28 and heater body 20. Accordingly, the heater body 20 is shaped to form a matrix surface for the head of the tack shaped cathode 28. The matrix surface may be contoured to provide more uniform temperature distribution on the surface 26 of the cathode thereby assuring proper emission characteristics. For further increasing thermal efiiciency, the heater voltage supply leads 22 may be attached to the heater body 20 at positions 32 near the heater matrix surface. This not only reduces the wattage required for achieving operating temperatures, but also reduces thermal losses by conduction throughout ceramic insulator 16 to the grid cup.

An alternative cathode structure as shown in Fig. wherein the connection tab 30 is an extension of a metal stamping 29 holding the cathode surface material 26. The stamped tab is held in contact with the cement layer 24 by means of bent arms 34 extending through apertures in the ceramic disc 16.

The insulator disc 16 may perform both insulation, heating and spacing functions as shown in Fig. 6. In this embodiment a single piece of ceramic has the integral ridges 18 as well as an integral heater body 20 extending on one side of the disc. In the manufacture of such a ceramic spacer the carbidizing process is effected selectively on the ridges 18 and heater 20 by masking off the desired insulating surfaces during exposure to a methane atmosphere, or by cooling the insulating section and heating only the projections. Accordingly, the heater body 20 functions to conduct electrical heating current whereas the carbidized ridges 18 become black body radiators to serve as means for thermally conducting heat away from the insulator disc 1.6 to thereby maintain a lower temperature and improve the performance of the cathode assembly.

Should a filamentary type emission surface be desired rather than the aforedescribed indirectly heated cathodes, a structure such as shown in the embodiment of Fig. 7 may be utilized. Here a filament heater 21 is suspended between the spacer ridges 18 adjacent to the grid aperture 12. If necessary, a tension loop 36 may be made in the filament structure to prevent sagging of the filament upon heating and thereby maintain a close dimensional tolerance also in this embodiment.

It is clear from the foregoing description of the invention and its method of construction that a novel and eflicient cathode assembly is provided offering many advantages from prior art devices. Accordingly, those 4 features believed descriptive of the nature of the invention are defined with particularity in the apppended claims.

I claim:

1. The combination of an insulating spacer disc having integral ridges, a cathode heater assembly affixed to said disc comprising a heater body and a tack shaped metallic cathode intimately contacting the heater body, a metallic grid aperture cup, and means affixing said spacer disc and said cup together by shoulders impressed into the walls of said cup to establish a close dimensional spacing between said cathode and the grid aperture by holding said integral ridges on said spacer disc in contact with the bottom of said aperture cup.

2. In combination, an electrode aperture cup, an insulator disc body having integral spacer ridges thereon for spacing the disc inside said cup, means in the walls of said cup for holding said spacer sections against the bottom of said cup to thereby establish a fixed distance between the ceramic disc body and the aperture, and a cathode heater assembly cemented to said disc body to thereby establish a precise cathode to aperture spacing comprising a carbidized ceramic heater cemented in an aperture in said disc, and a cathode with an emitting coating is thermally secured to said heater.

3. A combination as defined in claim 2 wherein the cathode comprises a stamper metallic tab and means fastening said tab to a fixed position in relation to said ceramic body and wherein the heater comprises a body cemented to both said disc body and said cathode assembly.

4. A combination as defined in claim 2 wherein the heater comprises a carbidized ceramic body cemented to said disc body, and the cathode comprises a tack shaped base of conductive material thermally contacting said heater at the shank side of the head and having a thermionic emission material coating the other side of said head.

5. A thermionic cathode assembly comprising a ceramic disc having at least one integral spacer ridge, a tack shaped base of conductive material having a thermionic emission material intimately coated upon the head of the base, a cathode heater body aflixed to the disc and comprising a curvilinear indentation sloping from a recessed central portion to shallower edge portions, and a mating surface on the back of the coated head of the base shaped to substantially contact the indentation over the entire surface to thereby comprise a matrix surface for providing thermal contact between said base and said heater body.

6. An indirectly heated cathode assembly comprising an electrically conductive heater body, a thermal and electrically conductive cathode base thermally contacting said heater body at a matrix surface, and an emissive material coated upon a surface of said cathode base remote from said matrix surface.

7. A cathode construction for a thermionic tube comprising a member providing an electron emitting surface, an electrically conductive heater body in intimate thermal contact with said member, an insulating element provided with an aperture receiving said heater body having annular ridges about said body, a grid aperture assembly enclosing said heater body and spaced therefrom by said ridges, and means fixing said grid aperture assembly to said insulating element.

8. In combination, a grid aperture assembly, an insulator disc body supported a fixed distance from said grid aperture assembly, a heater body fastened to said ceramic body and a cathode comprising a stamped metallic tab fastened to said disc by clamping means keeping said tab in intimate thermal contact with said heater body.

9. The combination of an insulating member of porous ceramic material including projections on one side comprising at least one integral spacer ridge and a heater body, said member having a portion including at least the projecting part of the heater body carbidized to thereby provide an electrically conductive heating medium therefor, means for applying an electric current to the carbidized portion of the heater body to heat the same, and thermionic emission material carried by the carbidized portion of the heaterbody in thermal responsive relation thereto.

10. A cathode assembly as defined in claim 6 wherein the electrically conductive heater body comprises an insulating body of porous ceramic material in the form of a disc presenting at one side thereof both a spacer ridge and the heater body projected from the surface of the disc, said insulating body having a portion thereof having its pores impregnated with electrically conducting material to thereby operate as said electrically conductive heater body in response to applied current.

11. A heater-cathode assembly comprising a cup-shaped carbidized ceramic heater element, said heating element having an aperture in the closed end thereof, a disc-like electrically conductive element, lead means electrically secured to said conductive element and extending through but being electrically insulated from said aperture, one surface of said conductive element being thermally bonded to but electrically insulated from the closed end of said heating element, and an electron-emissive coating on the opposite surface of said conductive element.

12. A heater-cathode assembly comprising a cup-shaped carbidized ceramic heater element, the closed end of said heater element having a concave surface, a conductive element having a plane surface and a convex surface, said convex surface being substantially complementary to the concave surface of said heater element,

said convex surface being thermally bonded to but electrically insulated from said concave surface, an electron emissive coating on said plane surface, and separate lead means electrically secured to said heater element and said conductive element.

13. A heater-cathode assembly comprising a tube-like carbidized ceramic heater member having a closed end,

a button-like conductive element, saidelement having an electron emissive coating on one surface thereof, another surface thereof being thermally bonded to but electrically insulated from said heater member, and separate leads electrically secured to both said heater member and said conductive element. 7

14. A heater-cathode assembly in accordance with claim 13 wherein the lead which is secured to said conductive element passes through an aperture in the closed end of said heater member and is electrically insulated therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 1,881,644 Jones Oct. 11, 1932 2,108,544 Meyer Feb. 15, 1938 2,125,418 Benjamin Aug. 2, 1938 2,171,766 Ruska Sept. 5, 1939 2,184,821 Uhlmann Dec. 26, 1939 2,244,356 Bucklin June 3, 1941 2,244,358 Bwald June 3, 1941 2,310,811 Schantl Feb. 9, 1943 2,378,569 Messner June 19, 1945 2,456,474 Wainwright Dec. 14, 1948 2,462,921 Taylor Mar. 1, 1949 

